The objectives of this proposal is to prepare xenoantisera, in rabbits, and monoclonal murine antibodies reacting with defined membrane antigens of functional subclasses of human thymus-dependent lymphocytes (T cells). T lymphoblastoid lines, peripheral blood T cells, blast and non-blast T cells, alloantigen binding and non-binding T cells isolated from primary and secondary mixed lymphocyte responses, and T blast cells responding to PPD are being used to prepare immunogens. Animals will be immunized with whole viable cells, cell membranes, and detergent-solubilized cell membranes. Solubilized membranes will be purified prior to immunization by negative selection, initially by removing irrelevant antigens shared by T and B lymphocytes, using affinity columns with bound rabbit antibodies to B lymphoblastoid cell membrnaes. Antigens common to all T cells will eventually be removed from solubilized membranes of T cell subclasses prior to immunization, by affinity chromatography using antibodies to T lymphoblastoid cells. Antisera will be analysed serologically and functionally on all T cell populations. The antisera will also be characterized in terms of the nature of the antigen with which they react, by immunoprecipitation of detergent-solubilized membrnaes from the T cell populations labeled internally or externally, followed by analysis using polyacrylamide gel electrophoresis in SDS and isoelectric focusing in 6 M urea. Electrophoretic variants of the antigens, and alloantigenic variants detectable serologically will ultimately be sought.